1. Field of the Invention
The present invention relates to a method and device for the inspection of a substrate, and more particularly to the method and device for the inspection of defects inside a substrate and the inspection of contamination of the surface of a substrate.
2. Description of the Related Art
The current demand for improvements in the productivity and degree of integration of integrated circuits has resulted in a trend to both expanding the diameter of silicon wafers, which are single-layer substrates on which integrated circuits are formed, from the 200 mm of the prior art to 300 mm and reducing the width of lines making up the integrated circuits to the order of approximately 0.25 .mu.m.
The presence of defects such as foreign matters or contamination on the surface of the above-described large-diameter silicon wafers, however, has a serious effect when forming a large number of extremely compact integrated circuits. A silicon wafer on which integrated circuits are to be formed must therefore be examined as a sample substrate to discover defects on the surface and carry out corrections or countermeasures.
Methods for inspecting for defects on the surface of a sample substrate such as a silicon wafer include light scattering, SEM/EPMA (Scanning Electron Microscope/Electron Probe Microanalysis), and SEM/AES (SEM/Auger Electron Spectroscopy).
The surface of a sample substrate can be inspected for defects in any of the abovementioned methods of the prior art, but in each case, the construction of the apparatus is complex and of a large scale. In addition, analysis by these methods is complicated and time-consuming, and the addition of a substrate inspecting device to a circuit fabrication line to allow, for example, automatic inspection of sample substrates, has proven to be extremely difficult.
At present, multilayer substrates such as PWB (Printed Wiring Boards) are being used to form complex circuits at high density. A typical multilayer substrate is a circuit substrate in which films or layers of various materials such as copper, polyamide, glass, and epoxy are stacked as a single unit and through-holes are formed to allow conduction between the different layers.
Defects such as minute foreign matters or faults in wiring may easily occur when fabricating this type of multilayer substrate because many processes are used to form the microscopic structures. For example, particles of material that are produced in processes involving cutting or grinding may easily adhere to the processed surface as foreign matters, and mask material such as photoresist in photo-etching processes also tends to remain on the surface.
These types of defects are difficult to completely eliminate despite cleaning of the surface after each process to prevent such defects. The sampling inspection of completed multilayer substrates to detect defects and analyze the causes of defects is crucial for raising yield, but defects may also easily occur inside the substrate because multilayer substrates are formed by successively stacking a large number of layers and films, and the inspection of defects in the interior of a completed multilayer substrate is difficult.
When inspecting for the presence of defects in this type of multilayer substrate, wires are conventionally connected to the many terminals of the completed multilayer substrate and current is actually conducted to each part of the multilayer substrate. When the existence of a defect is determined in this inspection, the location of the defect is determined, the multilayer substrate is cut, and when the defect is found, the material and construction are analyzed. In the above-described method of inspecting a substrate, wires must be connected to the many terminals of the completed multilayer substrate to actually conduct electricity to each part. Moreover, once a defect that has been determined to exist, the position must then be determined, and the multilayer substrate must be cut repeatedly until the defect is actually found.
The prior-art method of inspecting a substrate therefore entails the demanding tasks of first determining whether a defect exists inside a multilayer substrate and then determining the position of the defect. As a result, the method of the prior art requires considerable time and is difficult to automate.